Effect of deep inhalations after a bronchial methacholine provocation in asthmatic and non-asthmatic subjects

Deep inhalations cause a transient relaxation of the peripheral airways smooth muscles in non-asthmatic subjects. It has been claimed that the airway response to deep inhalations may be different in asthmatic subjects in whom deep inhalations should rather cause bronchoconstriction. The aim of the present study was to find out whether deep inhalations discriminate between asthmatic and non-asthmatic subjects with pre-constricted airways, using a methacholine provocation test protocol with deep inhalations following the last dose of methacholine. In 164 adults, a methacholine provocation was performed. Directly after the FEV1 measurement at the highest metacholine concentration, the subjects took one deep breath and another three deep inhalations 20 s later. One minute after the inhalation of the highest concentration FEV1 was measured twice. Thirty-three asthmatics PD20FEV1 = 0.24 mg (0.13-0.39) (median, 25-75th 75th percentiles) and 131 non-asthmatics PD20FEV1 = 2.05 mg (0.72-10.1) participated. The mean maximal decrease in FEV1 after the provocation test was 36% in the asthmatics and 27% in the non-asthmatics. Corresponding values after the deep inhalations were 18% in the asthmatics and 12% in the non-asthmatics. In conclusion, deep inhalations attenuate the methacholine-induced bronchoconstriction in both asthmatic and non-asthmatic subjects. Thus, the effect of deep inhalations did not discriminate between asthmatic and non-asthmatic subjects.